为什么我的列表在重新排列项目后没有重建

Question

这是使用 Flutter 和 Provider 包的玩具应用。我的目标很简单： - OuterProvider 有用于构建列表的数据 (ListView.builder) - Outer provider 有 Shuffle 按钮，可以随机播放内部列表 - 内部小部件 (Rows) 使用 InnerProvider 进行随机更改数据

当我点击InnerWidget - 提供者正确更新数据 但是当我洗牌数据时，即使数据被洗牌。构建方法已运行，但我的小部件列表不受影响...。

这里是示例代码

import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:flutter/foundation.dart';
import 'dart:math';

class InnerProvider extends ChangeNotifier {
  int pid;
  InnerProvider(this.pid);

  get id => pid;

  set id(int i) {
    pid = i;
    notifyListeners();
  }
}

class OuterProvider extends ChangeNotifier {
  List _data = [
    InnerProvider(1),
    InnerProvider(3),
    InnerProvider(4),
    InnerProvider(5),
  ];

  get data => _data;

  addToData(var item) {
    data.add(item);
    notifyListeners();
  }

  reShuffle() {
    data.shuffle();
    notifyListeners();
  }

  changeId(var i) {

    var dtIndex = _data.indexOf(i);
    _data[dtIndex].id = Random().nextInt(99);
  }
}

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider<OuterProvider>(
        create: (_) => OuterProvider(),
        child: MaterialApp(
          title: 'Flutter Demo',
          theme: ThemeData(
            primarySwatch: Colors.blue,
          ),
          home: MyHomePage(title: 'Why this does not work?'),
        ));
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  List outerData;

  void reShuffleData() {
    Provider.of<OuterProvider>(context).reShuffle();
  }

  @override
  Widget build(BuildContext context) {
    outerData = Provider.of<OuterProvider>(context, listen: true).data;
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
          child: ListView.builder(
              itemCount: outerData.length,
              itemBuilder: (context, int i) {
                return ChangeNotifierProvider<InnerProvider>(
                    create: (_) => outerData[i], child: InnerChild());
              })),
      floatingActionButton: FloatingActionButton(
        onPressed: reShuffleData,
        tooltip: 'Shuffle',
        child: Icon(Icons.add),
      ),
    );
  }
}

class InnerChild extends StatelessWidget {
  Widget build(BuildContext context) {
    var prov = Provider.of<InnerProvider>(context);
    return Row(mainAxisAlignment: MainAxisAlignment.center, children: <Widget>[
      GestureDetector(
          onTap: () {
            Provider.of<OuterProvider>(context).changeId(prov);
          },
          child: Text(
            Provider.of<InnerProvider>(context).id.toString(),
            style: TextStyle(fontSize: 40),
          )),
    ]);
  }
}

Answer 1

以下是工作代码。您正在使用默认值并且没有使用更改。请参考下面的代码。

已编辑

对于这个用例，您应该使用ChangeNotifierProvider.value 而不是ChangeNotifierProvider。 Difference

import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:flutter/foundation.dart';
import 'dart:math';

class InnerProvider extends ChangeNotifier {
  int pid;
  InnerProvider(this.pid);

  get id => pid;

  set id(int i) {
    pid = i;
    notifyListeners();
  }
}

class OuterProvider extends ChangeNotifier {
  List _data = [
    InnerProvider(1),
    InnerProvider(3),
    InnerProvider(4),
    InnerProvider(5),
  ];

  get data => _data;

  addToData(var item) {
    data.add(item);
    notifyListeners();
  }

  reShuffle() {
    data.shuffle();
    notifyListeners();
  }

  changeId(var i) {

    var dtIndex = _data.indexOf(i);
    _data[dtIndex].id = Random().nextInt(99);
  }
}

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider<OuterProvider>(
        create: (_) => OuterProvider(),
        child: MaterialApp(
          title: 'Flutter Demo',
          theme: ThemeData(
            primarySwatch: Colors.blue,
          ),
          home: MyHomePage(title: 'Why this does not work?'),
        ));
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  List outerData;

  void reShuffleData() {
    Provider.of<OuterProvider>(context).reShuffle();
  }

  @override
  Widget build(BuildContext context) {
    outerData = Provider.of<OuterProvider>(context, listen: true).data;
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
          child: ListView.builder(
              itemCount: outerData.length,
              itemBuilder: (context, int i) {
                return  ChangeNotifierProvider<InnerProvider>.value(
                  value: outerData[i],
                  child: InnerChild(),
                );
              })),
      floatingActionButton: FloatingActionButton(
        onPressed: reShuffleData,
        tooltip: 'Shuffle',
        child: Icon(Icons.add),
      ),
    );
  }
}

class InnerChild extends StatelessWidget {
  Widget build(BuildContext context) {
    var prov = Provider.of<InnerProvider>(context);
    return Row(mainAxisAlignment: MainAxisAlignment.center, children: <Widget>[
      GestureDetector(
          onTap: () {
            Provider.of<OuterProvider>(context).changeId(prov);
          },
          child: Text(
            Provider.of<InnerProvider>(context).id.toString(),
            style: TextStyle(fontSize: 40),
          )),
    ]);
  }
}